An optical circulator device is a special fiber-optical element able to separate optical signals traveling in opposite directions in an optical fiber. An optical circulator is a three-port device designed in a manner to ensure light entering any port will exit from the next port. FIG. 1 shows a schematic view of a known passive optical circulator. As shown in FIG. 1, a passive optical circulator 101 has three ports, namely, the first port, the second port and the third port, with each of ports connected to an optical connector 102, 103, 104, respectively. For light entering from optical connector 102 to the first port, the light will exit from the second port to optical connector 103. Similarly, light entering optical connector 103 to the second port will exit from the third port to optical connector 104. With low insertion loss and high isolation between ports, optical circulators are often used to achieve bi-directional transmission over a single fiber in communication systems.
However, the passive optical circulators can only be used with a specific type of optical connector, namely, APC-type connector, to prevent the entering light from back-reflection (BR) at an exit port. When the passive optical circulator is used with UPC-type or PC-type optical connector, severe back-reflection at the optical connector can be detected to render the passive optical circulator relatively ineffective when using with UPC-type or PC-type optical connector, and the application of passive optical circulator is often restricted to APC-type optical connector. However, with the rapid changes and improvement in hardware devices and optical fiber system deployment, the optical-based application systems often includes various connectors, such as, APC-type, UPC-type and PC-type connectors. Therefore, it is imperative to devise an optical circulator device able to be used with UPC-type and PC-type connectors to accommodate the deployment with mixed connector types.